Sheryl Sandberg fails to realise that what she simply considers Facebook's "poor communication" about its psychological experiments (Facebook apologises for experiments on users, 2 July) was an ethical violation of the principle of informed consent for 700,000 users. What makes this experiment more grievous is the lack of a briefing or debriefing, as well as a callous disregard for the principle to avoid harm to subjects. By manipulating the emotions of hundreds of thousands of Facebook users, and not telling them their emotions were impacted by an experiment rather than their own failings or temperament, Facebook has probably caused some real psychological harm to some of its users.Carter BraceEgham, Surrey

• My husband and I own a small restaurant in Sheffield. It has been our life's work (so far). We worked hard to set up our small but thankfully busy and (we think) good South American steak house. It is our livelihood and the only source of income we have to support ourselves and our young son. In terms of what we have created it's on a small scale but nevertheless helpful to society – we employ 15 full-time and three part-time staff, and we pay rates, VAT and taxes.

Yet I am totally demoralised every time a keyboard warrior with no professional accreditation takes to the likes of TripAdvisor and now Facebook and Twitter to rubbish our whole business. And there is nothing we can do about it. We can't opt out of TripAdvisor.

Can you imagine an international forum where you can review how awful your co-worker was on one particularly bad day they were having, or even just in one encounter with you, for their potential future employers to be able to check? Our future employers are our potential customers – and they're checking us out on TripAdvisor and Facebook. If only more people understood the other side of those reviews.Gloria ClarkeSheffield